Electronic signal monitoring techniques are widely used in modern applications, including surveillance applications. The goal of electronic signal interception and monitoring is to detect and extract basic meta-data about a signal, which can indicate the type or classification of the transmitter.
One type of signal monitoring system divides a surveyed spectrum into slices. Each slice of the spectrum is monitored by a single multi-bit analog-to-digital converter (ADC) in a different channel. Each channel samples an un-aliased slice of the surveyed spectrum. This technique can be performed using spectrum translation of each slice to baseband with appropriate channel filtering. The disadvantage of this system is high cost, due to the requirement to implement multiple high-quality channels, with each channel having an ADC.
Another type of signal monitoring system uses under-sampling with band-pass filtering to suppress all out-of-band spectral content. However, this solution still requires multiple high-quality channels to cover a wide frequency spectrum, with each channel having an ADC.
Yet another type of signal monitoring system uses a single-bit receiver for surveillance of a wide instantaneous bandwidth. The single-bit receiver is used in a first step of detection. Once the single-bit receiver is detecting a signal of interest, the single-bit receiver provides detected signal frequency information directly to a higher-quality multi-bit receiver. The multi-bit receiver is then tuned to the signal that was first detected by the single-bit receiver. This scheme has an inherent limitation of a lag in time between the actual signal appearance and the final examination of the signal using the high-quality multi-bit receiver. Critical information in the monitored signal may be missed during the tuning time of the multi-bit receiver.